Spa



FIG. 1 is a top perspective view of a spa, showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a left side view thereof, the right side view being identical thereto; and,

FIG. 4 is a front view thereof, the back view being identical thereto.

The broken line showing is for illustrative purposes only and forms no part of the claimed design. 

I claim the ornamental design for an spa, as shown and described. 